Abstract Detail

The negotiated surveillance of parts and wholes: a symbioses-centered perspective on plant biology research

Bogar, Laura M. [1], Peay, Kabir G. [1].

What stabilizes the ectomycorrhizal mutualism? An experimental test of partner choice by Pinus muricata in association with Suillus brevipes.

Most temperate forest systems are dominated by plants that rely upon ectomycorrhizal fungi for their nutrition. Ectomycorrhizal relationships can be thought of as trading agreements between plants and fungi: Plants provide carbon fixed by photosynthesis in exchange for nitrogen, phosphorous, and other trace nutrients that fungi scavenge from the surrounding soil. In most cases, this metabolic marketplace helps both partners acquire the goods and services they need. It remains unclear, however, what keeps this market stable. One mechanism that could stabilize these interactions is preferential allocation of resources to the best available plant or fungal partner. It is known that arbuscular mycorrhizal plants and fungi are capable of this kind of regulation, but it is not clear if ectomycorrhizas operate in a similar way. To test this hypothesis, we manipulated partner quality in a split-root experiment using Pinus muricata (Bishop Pine) seedlings and Suillus brevipes (Slippery Jack) fungi. We controlled partner quality by planting separate chambers with hyphal ingrowth bags containing either sand (low quality) or a mixture of sand and casein (high quality) After ten weeks, pines will be labeled with ¹³CO₂ and carbon allocation to each root compartment will be measured using isotope mass spectrometry. Although both root compartments have the same fungal genotype, the fungus with access to protein is expected to provide more nitrogen to the plant than the fungus with only a sand bag. If plants are able to allocate resources based on partner quality, we expect that plants will allocate more carbon to the fungi that have access to protein-filled bags than to the fungi that have access to the sand bags, and that this difference will be even more pronounced when the plant has a choice between one of each type. This result would demonstrate that the regulated exchange of photosynthetic carbon for soil-derived nitrogen in ectomycorrhizal associations does not require the plant to distinguish between fungal genotypes, and that that the trade can be controlled at fine spatial scales. Such finessed plant control of the ectomycorrhizal interaction may be a mechanism contributing to ectomycorrhizal fungal community composition in the field, and could help explain the persistence of this widespread mutualism.

1 - Stanford University, Department of Biology, 371 Serra Mall, 227 Herrin Labs, Stanford, CA, 94305, USA

Keywords:
Biological markets
cooperation
Fungi
Stable isotope enrichment
symbiosis.

Presentation Type: Symposium Presentation
Session: SY16
Location: Salon 4/The Shaw Conference Centre
Date: Wednesday, July 29th, 2015
Time: 9:15 AM
Number: SY16004
Abstract ID:1086
Candidate for Awards:None